The present invention relates to a stage position control method and a stage position control apparatus for a stage device, and more particularly relates to a stage position control method and a stage position control apparatus applied to a stage device driven in the X-axial and Y-axial directions.
Known examples of such stage position control apparatuses are stage position control apparatuses comprising a Proportional Integral Differential (hereafter referred to as PID) controller, and stage position control apparatuses comprising the PID controller and a Feed Forward (hereafter referred to as FF) controller.
Such stage position control apparatuses have the problem that capabilities regarding constant speed, positioning precision, etc., deteriorate due to disturbances owing to tension and the like in power supply cables and signal transmission cables. Of these, with regard to signal transmission cables, disturbances owing to tension occur due to the following reasons. The signal transmission cables must be joined between a moving portion and a fixed portion of the stage device. The signal transmission cable has flexibility, and deforms to follow the movement of the stage whenever the stage moves. However, deforming of the signal transmission cable affects the movement of the stage, however slight. In other words, the tension of the signal transmission cable affects the control system as disturbance. This is also true in the event that a guide mechanism of the stage has static pressure bearings. That is, in the event that static pressure bearings are used, the moving portion and the fixed portion of the stage device must be connected with a flexible pneumatic tube.
Increased control gain for the control system might be considered to reduce the effects of such disturbance. However, there is a limit to how high the control gain can be, and in actual practice, speed fluctuations and position error occur due to such disturbance.
Accordingly, it is an object of the present invention to provide a stage position control method applied to stage devices which are components of machine tools, semiconductor manufacturing apparatuses, measurement equipment, and other such industrial equipment, which is capable of improving the positioning precision and speed stability of the stage.
Another object of the present invention is to provide a stage position control apparatus suitable to the above stage position control method.
The stage position control method according to the present invention is applied to a stage device comprising a stage, a driving axis which mounts the stage and is driven in one axial direction, and first and second driving units for performing translational driving of the driving axis independently at two positions. In the stage position control method, the amount of movement of the first and second driving units are detected by first and second position detecting units, respectively, and the first and second driving units are controlled by first and second feedback control systems.
According to a first aspect of the present invention, the first feedback control system outputs a translational thrust command value to the first and second driving units by receiving an average value of each position detecting value measured by the first and second position detecting units as a position feedback value of the stage translational direction. The second feedback control system receives a difference between each position detecting value as a position feedback value of the stage yawing direction, and outputting a yawing direction thrust command value to the first and second driving units. Thus, the motion of the stage is divided into translational direction motion and yawing direction motion, and independently controlled and compensated thereby.
The stage position control apparatus according to the present invention is applied to the above stage device. The amount of movement of the first and second driving units are detecting by first and second position detecting units, respectively. The first and second driving units are controlled by first and second feedback control systems, respectively.
The stage position control apparatus comprises a coordinate converting block for calculating an average value from each position detection value measured by the first and second position detecting units and outputting the result to the first feedback control system as a position feedback value of the stage translational direction, and also calculating a difference between the each position detection value and outputting the result to the second feedback control system as a position feedback value of the stage yawing direction. The first feedback control system comprises a first subtracter for calculating a difference between a stage translational direction position command value and the stage translational direction position feedback value, a first PID compensator which receives the difference calculated at the first subtracter as the input thereof and outputs a thrust target value, a disturbance observer which computes estimated disturbance force for the stage, based on a translational thrust command value calculated from the thrust target value and on stage translational direction position feedback value, and a second subtracter for calculating a new translational thrust command value by subtracting the estimated disturbance for the stage from the thrust target value, and outputting the new translational thrust command value to the first and second driving units. The second feedback control system comprises a third subtracter for calculating a difference between a stage yawing direction command value and the stage yawing direction position feedback value, and a second PID compensator which receives the difference calculated at the third subtracter as the input thereof and outputs a yawing direction thrust command value to the first and second driving units.
The present invention is suitably applied to a driving axis (gantry axis) comprising independently-controlled first and second driving units and first and second position detecting units being positioned across a certain distance. According to the present invention, occurrence of error due to yawing of the stage can be suppressed, and compensating for disturbance acting on the stage allows positioning precision of the stage to be improved.
Also, dividing the movement of the stage into translational movement in one axial direction and yawing movement, and controlling and compensating accordingly, allows not only the translational movement precision but the yawing movement precision of the stage to be improved, as well. Further, regarding the translational movement, estimating and compensating for the disturbance torque acting on the driving axis allows fluctuations in speed and position of the stage to be suppressed.